Annular Joint Design Help

[amoncur]

I've read that the mating force calculated for an annular joint is typically much higher than what is actually required to assemble the parts (because the calculated value assumes a true axial assembly, while a manual assembler will always be off axis, making it easier to assemble the parts). My question is, how much higher? For example, if I calculate x pounds to assemble two components, will the actual mating force be .1x? .5x? etc...

 

[MikeHalloran]

Please tell me where you read that.




Mike Halloran
Pembroke Pines, FL, USA

 

[amoncur]

In the Bayer design guide for annular joints - seems like a reputable source, no? You can find the guide on Bayer's website ("Snap-Fit Joints for Plastics")

 

[MikeHalloran]

Well, now that you've revealed that the context is snap fits for plastics, yes, it makes sense.

I think the important point is that you need to use the calculated force in designing assembly tools, but recognize that manual manipulation can assemble the typical joint with less effort. How much less, I don't know, and I'm not sure how one would measure it. I guess you'd need an instrumented hand.





Mike Halloran
Pembroke Pines, FL, USA

 

[amoncur]

That's what I figured. Thanks, anyway!

 

[btrueblood]

What if you deliberately designed assembly tools for non-axial insertion?

 

[MikeHalloran]

That's sort of what robotic wrists with 'remote center compliance' do. Since a robot can't always position a part at the same point in space, and since the fixtured part's mating feature may not always be at the ideal position, RCC tooling allows you to program the robot to put the part close to where it should be, then give it a little wiggle while pushing it. ... exactly as a human might do.

Better to design the parts with gentle lead-in chamfers.



Mike Halloran
Pembroke Pines, FL, USA

 

[amoncur]

Does anyone have experience using Polycarbonate for an annular joint? That's what the customer wants to use, but it seems like too rigid a plastic for an annular joint. What are your opinions? Optical clarity is the reason for the PC choice.

 

[MikeHalloran]

If you're intending to 'eyeball' the design, you might have a bad experience with PC.

If you bother to actually calculate the stresses associated with your dimensions and tolerances and stay within reasonable limits, and check for chemical compatibility, you should have no problem.



Mike Halloran
Pembroke Pines, FL, USA

 

[amoncur]

I've done the calcs, I'm just not sure how large of a difference I'll see between theoretical axial assembly, and practical manual. Ultimately I think it will be an iterative process.

Anyone else have experiences with PC annular joints? The material still worries me for this applications.

 

[MikeHalloran]

Why not put a dimensioned drawing of your joint with material specs in our "Plastics" or "Plastics Design/Tooling" forums and ask our experts for help?



Mike Halloran
Pembroke Pines, FL, USA